Year	Number of
1990	4.33
1991	4.52
1992	4.69
1993	4.85
1994	4.98
1995	5.3
1996	5.65
1997	5.93
1998	6.23
1999	6.72
2000	7.53
2001	8.16
2002	8.88
2003	9.37
2004	10.11
2005	10.81
2006	11.48
2007	12.06
2008	12.83
2009	13.27
2010	13.5
2011	13.81
2012	14.16
2013	14.55
2014	14.97
2015	15.42
2016	15.86